Tunable magnetron



Sept. 4, 1951 C. BECKER TUNABLE MAGNETRON Filed Aug. 30, 1946 EXTERNALLY APPLIED CONTROL SIGNAL Y R E ,M N R 0 EQJ m M WW M B Patented Sept. 4, 1951 'IUN ABLE MAGNETRON Carl W. Becker, Arlington, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application August 30, 1946, Serial N 0. 694,056

Claims.

This invention relates to electron-discharge devices, and more particularly to damping means for tunable electron-discharge devices.

While not limited thereto, the present invention is especially suitable for damping the tuning means used in electron-discharge devices of the -so-called magnetron type.

An object of this invention is to provide movable means, for tuning an electron-discharge device in response to an external signal, which is aperiodic or which changes its position by oneway movements and not by a series of oscillations.

Another object is to provide a movable electron-discharge tube tuning device with means for damping out the natural resonant frequency of said movable device, whereby overshooting of said device on quick movements is prevented.

A further object is to so design said damping means that its operation utilizes the leakage field already existing in an electron-discharge device of the magnetron type.

The foregoing and other objects of the invention will be best understood from the following description of some exemplifications thereof, reference being had to the accompanying drawing, wherein:

Fig. 1 is a fragmentary longitudinal sectional view taken substantially through the center of a tunable magnetron made in accordance with the principles of the invention;

Fig. 2 is an enlarged, fragmentary view of a portion of Fig. 1; and

Fig. 3 is an enlarged, fragmentary view, similar to Fig. 2, but showing a modified form thereof.

The present invention constitutes an improvement over that described in my copending application, Serial No. 586,969, filed April 6, 1945.

Referring, now, more in detail to one of the illustrative embodiments of the present invention, and with particular reference to Figs. 1 and 2 of the drawing showing the same, the numeral I generally designates an electron-discharge device of the so-called magnetron type.

Said device comprises an anode structure 2, a cathode structure 3, magnetic means 4 for establishing a magnetic field in a direction perpendicular to the path of the electron-flow between said cathode and anode structures, and

tuning means 5.

In the device shown, the anode structure 2 includes a cylindrical body 6 made of highly conductive material, such as copper, said body being provided with an interior, annular boss 6, in

turn provided with a multiplicity of radiallydisposed, interiorly-extending anode members in the form of vanes '1, each adjacent pair of said vanes, together with that portion of said cylindrical body lying therebetween, constituting a resonant line, preferably, a quarter-wave line whose output end is shorted, and whose natural resonant frequency is, as is well known in the art to which the present invention relates, a function of the geometry of the physical elements making up the same. The anode members I will be further described when referring, in a later portion of this specification, to the details of the tuning means 5.

The anode structure 2 is closed at its ends, for example, by end plates 8 and 6, with the junctions between the cylindrical body 6 of said structure, and said plates 8 and 9, hermetically sealed, as at Ill.

The cathode structure 3, which is coaxial with the anode structure 2, includes a cathode sleeve ll, conventionally made of nickel, or the like, provided with a reduced portion l2 whose length, preferably, is coextensive with the width of the anode members i, said reduced portion I2 being provided with a highly electron-emissive coating l3, for example, of the well-known alkalineearth metal oxide type.

In order properly to support the cathode sleeve II with respect to the anode members I, said sleeve may be reduced, as at It, to fit into an elongated, electrically-conductive tubular member I5. A glass seal (not shown) disposed within the tubular member l5, together with one or more glass beads (not shown) also disposed within said tubular member, supports a lead-in conductor 16 which passes through said member l5 and has its upper end connected, as at ll, to one terminal of a cathode heating filament IS. The other terminal of said filament may be connected, as at 19, to the cathode sleeve II.

In order to convey current to the filament 18, the lead-in conductor I6 is connected by a conductor (not shown) to one terminal of a suitable source of E. M. F. (not shown), the other terminal of said source of E. M. F. being connected by a suitable conductor (not shown) to tubular member l5.

Cathode 3 is supported with respect to the anode structure 2, and insulated therefrom, by any suitable means (not shown), such, for example, as shown in my copending application referred to above. Said supporting and insulating means may include a tubular bushing 26 secured to a tubular pole piece 2 I, constituting one of the components of the magnetic means 4.

Said pole piece 2| may be hermetically sealed, as at 22, into the end plate 8, and be provided with a central bore 23 whereby the cathode structure 3 may enter the device.

Another tubular pole piece 24 may be hermetically sealed, as at 25, into the end plate 9, said pole piece and the pole piece 2| being fixed, for example, to the. opposite ends of a horseshoe magnet 26 (only partially shown), whereby an appropriate magnetic field may be established, as previously indicated, in a direction perpendicular to the path of the electron-flow between the cathode structure 3 and anode structure 2.

Now; by suitably heating the cathode, and applying a proper potential between said cathode and the anode, the device can be made to generate electrical oscillations of a wavelength determined, primarily, by the capacitance and inductance built into said device as a function of the geometry thereof, and more-especially, of the dimensions of theabovereferredto resonant lines defined by the anode structure.

In order to extract power from the device I may, for example, introduce a loop 21 intov any one of thespaces defined by any two adjacent anode members 'I, said loop coupling with the magnetic component of the above-mentioned electrical oscillations. Said loop may,.in turn, be connected to a conductor 28 supported in a glass seal 29 fused into an. outlet pipe 30, said pipe being threaded and hermetically sealed into i the cylindrical body 6 ofthe anode structure 2. Each anode member i is provided with a slot 3| adapted to receive concentric conducting straps 32 and-33 which are, in turn, adapted alternately to contact successive anode members. Said straps present a capacitance therebetween which enters into the determination of the natural resonant frequency of'the device, and when the anode members are. thus inter-connected, spurious oscillations which may be. present are suppressed.

It has been found that, by moving another conducting member with respect to' the anode members 'i, or with respect to thestraps 32 and" 33 thereof, the'distributed capacitance, or, with appropriate modifications, the distributedinductance, of the device, or both, may be. altered whereby said devicemay be tuned to frequencies other than the natural resonant frequency thereof.

Saidadditional conducting member is provided in the form of an annular flange 34formed. at the lower. end of a hollow, cylindrical core or reed 3'5. Said core ispreferably made of a conducting material which has a relatively high Youngs modulus, such as Ni'chrome, so that the core is stiff and when'mounted has a relatively high natural resonant frequency. Said core or reed depend'sfrom a'fiexible diaphragm 36 which is secured, at its periphery, to a supporting ring 31, mounted within the body 6 upon the ledge presented by the boss 6 thereof. Wound upon thecore' and firmly secured thereto is a coil 38 of insulated wire, one end, 38', of said 0011 being electrically connected to the core, and the other end thereof passing through an opening 39 in the diaphragm 36, and-out of the device, through a glass seal 40 fused into a pipe 4| which is hermetically sealed into the end plate 9.

The core 35 and the coil 38 carried thereby should be so disposed with respect to the pole piece 24 thatsaid coil is within the leakage field existing between said pole piece 24 and the pole piece 2 I. Hence, upon application of an'external tioning (as a damping means) distributed capacitance of the device, and a consequent tuningthereof.

In the device as thus far described, there is no provision for damping or braking the movements of the core or reed 35. As a consequence, when said reed is moved rapidly, it has a tend ency to.overshoot:-that is, to go beyond its new rest position, after which it executes a series of mechanical'oscillations, at its natural mechanical resonant frequency, about its new rest position, before it finally comes to rest at said position.

'lnorder to eliminate or eradicate these movements, I proceed as follows:

.Core 35 has mounted thereon,,below coil 38 but. within the leakage magnetic field. of. the device I,,a continuous metallic. ring 44 prefer.- ably of. copper, which acts as ashort-circuited turn or. damping ring. When core 35 movesin the leakage field of the device, ring 44 moves therein also, causingeddy currents to. be. pro.- duced in. said ring, which. currents, due to. the extremely low resistance of said ring, produce an appreciable force which opposes the motion of the ring. Therefore, ring 44 acts asa'magnetic brakeor damping means for movements. of core 35, serving to damp vibrations or oscillationsof the core at its resonant frequency; as aresult, the core. is rendered aperiodic, so that on quick movementsthereoflit will not overshootits new rest position, but will change from its old to its new rest position by. a one-way movement: and not by'a series of oscillations. 'The movements of the core are not damped to any noticeable extent by the, material. of the. core. itself, because the high resistance of Nichrome prevents the setting up of any, substantial eddyv currents therein.

Asa result of the aperiodicv characteristicsrof the'moving tuning, means, when themagnetron output is being frequency-modulated by; an'external signal, spurious frequency, changes, which might beset up by oscillations of the moving core at its mechanical resonant frequency, are eliminated.

In the modification shown in Fig. 3 of: the 7 drawing, the electron-discharge: device I is essentially the same asthat shown in Figs. land 2, and like parts have been designated withlike reference numerals.

The difference betweenthese two embodiments is in the dampingmeans. In themodifieddamping means of Fig.3, thecoil 38, is woundon a. copper bobbin 45, which. bobbin is. in the leakage field of the device I.; the bobbin 45. with the winding-thereon is slipped over the Nichrome reed. or. core 35.

Like the. damping ring 44, the. bobbin 45 disposed withinthe leakage field existing between the. pole pieces 2! and 24, and its mode of funcis, likewise,

similar.

This completes the description ofthe aforesaid illustrative embodiments of the-"presentinvention'. It will benoted from all of the .foregoing. that I have provided damping means, for

tuning means for. an electron-discharge device leakage field already existing in such devices; and which damps out the natural resonant frequency of the moving tuning means, to thereby eliminate spurious movements of said tuning means;

Of course, it is to be understood that this ill,- vention is not limited to the particular details as described above, as many equivalents will sugest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretion commensurate with the scope of this invention within the art.

What is claimed is:

1. The combination with an electron discharge device which incorporates a cathode, an anode spaced from said cathode, and means for establishing a magnetic field in a direction substantially perpendicular to the path of the electron flow between said cathode and said anode, said device producing oscillations having a natural resonant frequency determined by the configuration of said device: of means, supported within said device and movable with respect to said anode, for tuning said device to a frequency other than said natural resonant frequency; and means, supported within said device by said movable means, for damping the movements of said movable means.

2. The combination with an electron discharge device which incorporates a cathode, an anode spaced from said cathode, and means for establishing a, magnetic field in a direction substantially perpendicular to the path of the electron flow between said cathode and said anode, said device when energized producing oscillations having a natural resonant frequency determined by the configuration of said device: of means, supported within said device and movable with respect to said anode, for tuning said device to a frequency other than said natural resonant frequency; and additional highly electricallyconductive means, supported by said movable means within the path of the magnetic lines of force of said magnetic means, cooperable with said lines of force for damping the movements of said movable means.

3. The combination with an electron discharge device which incorporates a cathode, an anode spaced from said cathode, and means for establishing a magneticfleld between said anode and said cathode in a direction substantially perpendicular to the path of the electron flow between said cathode and said anode: of a reed, supported within said device and movable with respect to said anode, for tuning said device; and additional highly electrically-conductive means, supported by said reed and cooperable with said magnetic field, for damping the movements of said reed.

4. The combination with an electron discharge device which incorporates a cathode, an anode spaced from said cathode, and means for establishing a magnetic field in a direction substantially perpendicular to the path of the electron flow between said cathode and said anode: of a reed, supported within said device and movable with respect to said anode, for tuning said device; and additional highly electrically-conductive means, supported by said reed within the path of the magnetic lines of force of said magnetic means, cooperable with said lines of force for damping the movements of said reed.

5. The combination with an electron discharge device which incorporates a cathode, an anode spaced from said cathode, and means for ltab lishing a magnetic field in a direction substan tially perpendicular to the path of the electron flow between said cathode and said anode: of a reed, supported within said device and movable with respect to said anode, for tuning said device; means, supported by said reed within the magnetic lines of force of said magnetic means and receptive of an external signal, for establishing a signal-responsive magnetic field cooperable with said lines of force for controlling the movement of said reed; and additional highly electrically-conductive means, supported by said reed, for damping the movements of said reed;

6. The combination with an electron discharge device which incorporates a cathode, an anode spaced from said cathode, and means for establishing a magnetic field in a direction substantially perpendicular to the path of the electron flow between said cathode and said anode: of a reed, supported within said device and movable with respect to said anode, for tuning said device; a coil, supported by said reed within the path of the magnetic lines of force of said magnetic means and receptive of an external signal, for controlling the movement of said reed; and additional highly electrically-conductive means, supported by said reed, for damping the movements of said reed.

7. The combination with an electron discharge device which incorporates a cathode, an anode spaced from said cathode, and means for establishing a magnetic field in a direction substantially perpendicular to the path of the electron fiow between said cathode and said anode: of a reed, supported within said device and movable with respect to said anode, for tuning said device; a coil, supported by said reed within the path of the magnetic lines of force of said magnetic means and receptive of an external signal, for controlling the movement of said. reed; and a shorted turn of highly electrically-conductive wire, supported by said reed within the magnetic lines of force of said magnetic means, cooperable with said lines of force for damping the movements of said reed.

8. The combination with an electron discharge device comprising an evacuated envelope containing a cathode, an anode spaced from said cathode, and means for establishing a magnetic field in a direction substantially perpendicular to the path of the electron flow between said cathode and said anode, said device producing oscillations having a natural resonant frequency determined by the configuration of said device: of means, supported within said device and movable with respect to said anode, for tuning said device to a frequency other than said natural resonant frequency; and a short-circuited lowresistance electrical-conductor turn, supported by said movable means within said evacuated envelope and the path of the magnetic lines of force of said magnetic means, for damping the movements of said movable means.

9-. The combination with an electron discharge device comprising an evacuated envelope containing a cathode, an anode spaced from said cathode, and means for establishing a magnetic field in a direction substantially perpendicular to the path of the electron flow between said cathode and said anode, said device producing oscillations having a natural resonant frequency determined by the configuration of said device: of means, supported within said device and movable with respect to said anode. for tuning said egseay iw "devi'ce tqfa frqiiency'other than Said n-atuifal resbna nt'j frequency; means, supported by said mdvable means 'within Said 1 evacuated envelope fan'd' the path tithe-magnetic lines of force of saidffiiagnetic "nieansand deceptive -of an exf ternal "signal; for establishing a Signal-responsive finagn'etic field cooberablewith Said"1ines"of "fcice ion-controlling the movement of 'said nfovable means; and a sh it-circuited low-resistance electr'ical conductor turn, supported by 'said movable *mean's' -with'in said evacuated envelbpe and the magnetic '1in'es of force of 'said magnetic means,

- fb'1 damping" the movements of said rn'o'vable rhfeans.

'IOJT he combination with an electron dischlarge device comprising an evacuated envelope cdntaining acathedean anode spaced from said fcathode, and means for establishing a magnetic j 'field in a direction"substantially perpendicular "to the-pa'th of the electron flow between said [cathode and said anode:- of a feed, suppcrted Within said device and movable with respectto feaid anode, for tuning said'device; a cbil, sup- "p'mted'by sa-id'reed'within the magnetic lines fef f orbebf Said Ifiag n'e'tic means aria receptive 6f n external siQriaL-io'rcontrolling the m'o'vement nee el'ecti'ical-cbnductor turn; supported by -said reed within said evacuated envelope and the path bf'the rhagnetic lines -'0f' f0r'ce of said magnetic means;--for-'-damping the movements of said reed.

cARL w'fBECKER.

, REFERENCES CITED iviTfieifo'l'lbwmg a1'e of record in the file ofthiy'patent:

V UNITED STATES PATENTS 

